There are real big difference between the ticket for a spectator, which can be used any time up until the game ends (the person can even show up just to watch the last 5 minutes if they want), and the ticket for a player who does not have the luxury of being able to show up toward the end of an event or whenever else they want like the spectator can. They are totally different products.
If they were able to resell your spectator seat to the football game to someone else they likely would, and there wouldn't be a thing wrong with it. There just isn't a practical way for them to be able to tell that you won't be attending until the game is already over though. Spectator seats and player entry spots are two totally different things with their own unique characteristics for when they are able to be used, and for when you are able to be able to tell that they aren't going to be used.
There are other big differences that necessitate treating a spectator seat differently than a player entry as well. Nobody cares if a seat ends up empty at the football stadium. However, if one of the teams doesn't have anybody to fill a position on the team, that is a much bigger deal. Seat 38 N in the stadium isn't filled. Ok, so what. One of the teams doesn't have a tight end. Now that's a much bigger deal. Likewise it is important that Mike resells any empty player slots because everybody would rather see as full of a field as possible rather than empty slots on the bracket. Having as many player slots filled in the tournament as possible also probably helps Mike in being able to market the event and attract as many vendors and spectators as possible, and get the best deal from the casino, etc. Being able to show (and then ultimately deliver) a full bracket (especially one that fills up in advance) goes a long way in a lot of ways with a lot of people.
As for reselling your ticket to somebody else, there are big differences between spectator tickets and player entry spots too. If you can't make the football game and you sell your seat to your neighbor Bob, nobody is going to care. The stadium or anybody else doesn't care in the least who shows up to fill your seat in the stadium, whether it is you, or your neighbor Bob, or even if nobody shows up to fill that seat at all. They do need to know that all the player positions are going to filled on the field though, and by who, as that is something that is much more important that people actually care about. Because of this the ticket sellers for the football game don't have to follow up to see who is going to end up in seat 38 N, or even if anybody is going to show up to fill that seat at all, and same thing with a spectator seat at the pool tournament. Different story when it is a player though. If you were able to sell you ticket to another player, Mike now has to go track down and speak with that player to confirm that he did indeed buy the spot and is going to play, because Mike can't chance having an empty slot in the player field. This is a hassle which he may want to minimize as much as possible, and this can be accomplished by having the no refund policy to ensure that only the people that are really serious about playing will sign up.
Aside from the hassle of dealing with the many substitutions that would likely occur if he allowed players to sell their spots, another reason he may not want to allow it is that he may want to be able to advertise who is going to be in the event, and then be able to deliver on it. If he advertises that Shane, Shaw, Efren and Earl are in the event, and then it ends up being Tom, Dick, and Harry and you in those spots instead, lots of people (fans, vendors, the host site, etc) are going to be disappointed and upset. The no refund policy ensures that who Mike advertised as being in the field is largely who ends up actually playing because it kept most of the tire kickers and people who weren't really sure if they would be able to make it or not from signing up. Other good reasons for having the no refund and no selling your entry spots policies have already been covered elsewhere in the thread.
